CN111837364A

CN111837364A - Transmitting/receiving device for bus system and method for reducing wired transmission

Info

Publication number: CN111837364A
Application number: CN201980018725.4A
Authority: CN
Inventors: S·沃克尔; S·施特格曼
Original assignee: Robert Bosch GmbH
Current assignee: Robert Bosch GmbH
Priority date: 2018-03-12
Filing date: 2019-03-05
Publication date: 2020-10-27
Also published as: EP3766213A1; DE102018203671A1; US11601301B2; EP3766213B1; US20200412573A1; WO2019174956A1

Abstract

A transmitting/receiving device (12) for a bus system (1) and a method for reducing wired transmission are provided. The transmission/reception device (12) comprises: a transmission stage for transmitting a transmission signal (TxD) to a first bus core (41) of a bus (40) of the bus system (1), wherein exclusive, collision-free access by a subscriber station (10, 20, 30) to the bus (40) of the bus system (1) is ensured at least at times in the bus system (1), and the transmission stage is used for transmitting the transmission signal (TxD) to a second bus core (42) of the bus (40); a receiving stage (12) for receiving bus signals (CAN _ H, CAN _ L) transmitted on the bus cores (41, 42); and a transmission reduction unit (15) for controlling the switch-on path of the first isolation device (1252) in the transmission stage depending on whether the dominant state (111) of the transmission signal (TxD) is present.

Description

Transmitting/receiving device for bus system and method for reducing wired transmission

Technical Field

The invention relates to a transmitting/receiving device for a bus system and a method for reducing wired transmissions. The bus system is in particular a CAN and/or CAN FD bus system. The transmitting/receiving device CAN be used in particular in CAN or CAN FD bus systems and uses switched isolation (Stand-Off) facilities in the transmitting stage, more precisely in the transmitting block of the transmitting stage, in order to bring about a reduction of the wired transmission.

Background

In the case of CAN bus systems, messages are transmitted by means of CAN and/or CAN FD protocols. The CAN bus system is used in particular for communication between sensors and control devices in vehicles or technical production plants and the like. In a CANFD bus system, data transmission rates of more than 1MBit per second (1 Mbps), e.g. 2MBit/s, 5MBit/s, or any other data transmission rate of more than 1MBit/s, etc., are possible. CAN-HS bus systems are also known (HS = high speed = Highspeed), in which data transmission rates of up to 500kbit per second (500 kbps) are possible.

For data transmission in CAN-bus systems, the CAN physical layer ISO11898-2:2016 of today needs to follow predetermined parameters as CAN protocol specification with CAN FD. In addition to following functional parameters, radiation (Emission), interference intensity (Direct Pin Injection — DPI (Direct Pin Injection)), and prevention of electrostatic discharge (ESD = electrostatic discharge) are considered.

The problems are that: in the case of CAN FD with 2Mbit/s and 5Mbit/s, the bit rate is increased by a factor of 4 or 10 compared to the conventional CAN in the case of 500kbit/s, however it is pre-given that even in the case of CAN FD the same transmission limits are followed as in the case of CAN. This is a significant challenge to meet the requirements for parameters that are compliant with wired transmissions.

The wired transmission of a CAN or CAN FD transceiver or a CAN or CAN FD transmitter/receiver is measured according to the 150 Ohm method (IEC 61967-4, Integrated circuits, Measurement of electromagnetic emissions,150 kHz to 1 GHz-Part 4: Measurement of connected emissions-1/150 direct coupling method (IEC 61967-4, Integrated circuit, Measurement of electromagnetic emissions,150 kHz to 1 GHz-Part 4: Measurement of wired emissions-1/150 direct coupling method)) and according to IEC62228 (EMC evaluation of CAN transceivers). In the case of a transmission measurement, the alternating voltage signal divided over the two bus lines (CAN _ H and CAN _ L) is evaluated.

The construction at the time of EMV measurement is specified in the document "IEC TS 62228 Integrated circuits-EMC evaluation of CANtransmitters". In this case, three transmitting/receiving devices are operated on the same CAN bus with a common 60Ohm terminating resistor and decoupling network. One of these transmitting/receiving devices transmits a transmit signal, and the other transmitting/receiving devices are in the same operating mode but do not transmit a dominant bit or dominant signal state, so that the transmit signal of these other transmitting/receiving devices is high = recessive (rezensv).

The technical challenge lies in: the required limit value (according to IEC 62228) is not exceeded in the case of wired radiation.

Disclosure of Invention

It is therefore the object of the present invention to provide a transmitting/receiving device for a CAN bus system and a method for reducing wired transmissions, which solve the aforementioned problems.

This object is achieved by a transmitting/receiving device for a CAN-bus system having the features of claim 1. The transmission/reception apparatus includes: a transmitting stage for transmitting a transmission signal to a first bus conductor of a bus of the bus system, in which exclusive, collision-free access by a user station to the bus of the bus system is at least sometimes ensured, and for transmitting the transmission signal to a second bus conductor of the bus; a receiving stage for receiving bus signals transmitted on the bus wires; and a transmission reduction unit for controlling a switch-on path of a first isolation (Stand-Off) device in the transmission stage according to whether a dominant state of the transmission signal occurs.

The described transmitting/receiving device is used to reduce radiation, in particular interference radiation, by a large amount, in particular by a few dB [ mu ] V. Thereby, wired transmission is reduced and electromagnetic compatibility (EMV) of the transmitting/receiving apparatus is improved. The invention contributes to reducing the emissions of the transmitting/receiving device in the case of a CAN-FD bit rate and provides a large contribution on the road following a limit value.

An increase in the symmetry of the two bus wires with respect to impedance can also be achieved.

As a further advantage, the described transmitting/receiving device results in: no additional capacitance is introduced on the bus wires of the bus lines for the bus. Instead, the transmitting/receiving device reduces the capacitance even with respect to a small signal.

The effect of the transmitting/receiving device is particularly advantageous when a common-mode choke is used, which typically has an inductance value of 100 muh, since in the case of this common-mode choke, in the case of conventional transmitting/receiving devices, particularly strongly excessively high radiation levels occur.

Further advantageous embodiments of the transmitting/receiving device are described in the dependent claims.

The emission reduction unit is especially designed to control the effective resistance with respect to ground for the on-path of the P-channel isolation device.

In one embodiment, the transmission stage has: a first transmission block for transmitting a transmission signal to a first bus core; and a second transmission block for transmitting the transmission signal to the second bus conductor, wherein the first isolation device is connected to the first transmission block.

It is conceivable that: the first isolation device is a P-channel isolation transistor, wherein the emission reduction unit is designed to control a gate of the P-channel isolation transistor.

It is also conceivable: and setting a second isolation device in the second sending block, wherein the second isolation device is smaller than the first isolation device in the first sending block. In this case, the second isolation device may be an N-channel isolation transistor.

According to a particular embodiment, the emission reduction unit has: a logic block for analyzing a transmission signal and a signal received from the bus; a resistor connected at one end to the gate of the isolation device and grounded at its other end; and a switch for switching the gate of the isolation device in dependence on the analysis result of the logic block, such that the gate of the isolation device is grounded either low-ohmic or high-ohmic via the resistance by means of the switch.

In this case, the logic block may be designed to: the switch is actuated to connect the switch-on path of the isolation device to low-ohmic ground when a dominant state of the transmit signal occurs, wherein the logic block is designed to: when a recessive state of the transmission signal occurs and the transmitting/receiving device of the subscriber station is operated for receiving but not transmitting, the switch is actuated in order to connect the on-path of the isolation device to ground with high resistance.

In this case, the switch may be a transistor having a resistance value lower than the resistance ohm, and wherein the output terminal of the logic block is connected to the gate of the transistor.

The transmission/reception apparatus may be a CAN FD transmission/reception apparatus.

The previously described transmitting/receiving device can be part of a bus system having a bus and at least two user stations which are connected to one another via the bus in such a way that they can communicate with one another. In this case, at least one subscriber station of the at least two subscriber stations has the previously described transmitting/receiving means.

The aforementioned object is also achieved by a method for reducing cable emissions having the features of claim 12. The method is carried out using a transmitting/receiving device for a bus system in which exclusive, conflict-free access to the bus of the bus system by a user station is ensured at least at times. In this case, the transmitting/receiving device has a transmitting stage, a receiving stage and a transmission reduction unit, wherein the method has the following steps: transmitting, with the transmit stage, a transmit signal to a first bus core of the bus; transmitting the transmit signal to a second bus core of the bus; receiving, by the receiving stage, bus signals transmitted on the bus cores; and with the transmission reducing unit, the switch-on path of the first isolation device in the transmission stage is controlled depending on whether a dominant state of the transmission signal occurs.

This method provides the same advantages as mentioned previously with respect to the transmitting/receiving apparatus.

Other possible implementations of the invention also include combinations of features or embodiments not explicitly mentioned before or below in relation to the embodiments. The person skilled in the art can also add individual aspects as improvements or supplements to the respective basic forms of the invention.

Drawings

Subsequently, the present invention is further described in terms of embodiments with reference to the accompanying drawings. Wherein:

fig. 1 shows a simplified block diagram of a bus system according to a first embodiment;

fig. 2 shows a circuit diagram of a transmitting stage of a transmitting/receiving device in a bus system according to a first embodiment;

fig. 3 shows a circuit diagram of a decoupling network for transmission measurements of a transmitting/receiving device in a bus system according to a first embodiment;

fig. 4 shows the waveforms over time of the instantaneous decoupled signal for transmission in the case of the first transmitting/receiving device according to the first embodiment;

fig. 5 shows the waveforms over time of the instantaneous decoupling signal for transmission in the case of the second transmitting/receiving device according to the first embodiment;

fig. 6 shows a frequency spectrum in the case of the first transmitting/receiving apparatus according to the first embodiment; and

fig. 7 shows a frequency spectrum in the case of the second transmitting/receiving apparatus according to the first embodiment.

In the drawings, the same or functionally same elements are provided with the same reference numerals unless otherwise specified.

Detailed Description

Fig. 1 shows a bus system 1, which may be, for example, at least partially a CAN bus system, a CAN FD bus system, or the like. In general, the bus system 1 is a serial bus system in which the bus state, in particular the dominant level of the transmit signal, is actively driven. The bus system 1 can be used in vehicles, in particular in motor vehicles, aircraft, etc., or in hospitals, etc.

In fig. 1, a bus system 1 has a plurality of

subscriber stations

10, 20, 30, which are each connected to a bus 40 having a first bus line 41 and a second bus line 42. In the case of a CAN bus system, the

bus lines

41, 42 are used for signals for CAN _ H and CAN _ L and for coupling in the transmit state to a dominant level. Via the bus 40,

messages

45, 46, 47 can be transmitted between the

individual user stations

10, 20, 30 in the form of the signals mentioned. The

user stations

10, 20, 30 can be, for example, control devices or display devices of a motor vehicle.

As shown in fig. 1, the

subscriber stations

10, 30 each have a communication control device 11 and a transmitting/receiving device 12. The transmission/reception devices 12 respectively include an emission reduction unit 15. And the subscriber station 20 has a communication control means 11 and a transmitting/receiving means 13. The transmit/receive means 12 of the

subscriber stations

10, 30 and the transmit/receive means 13 of the subscriber station 20, respectively, are connected directly to the bus 40, even if this is not shown in fig. 1.

The communication control means 11 are used to control the communication of the

respective subscriber station

10, 20, 30 with other subscriber stations of the

subscriber stations

10, 20, 30 connected to the bus 40 via the bus 40, respectively. The transmitting/receiving means 12 serve to transmit and receive

messages

45, 47 in the form of signals and in this case use the emission reduction unit 15, as will be described in more detail later on. The communication control device 11 CAN be implemented in particular like a conventional CAN-FD controller or CAN controller. In other cases, the transmitting/receiving means 12 may be implemented, in particular, like a conventional CAN transceiver and/or CAN-FD transceiver. The transmitting/receiving means 13 are used for transmitting and receiving messages 46 in the form of signals. In other cases, the transmitting/receiving device 13 may be implemented like a conventional CAN transceiver.

Fig. 2 shows the basic structure of the transmitting/receiving apparatus 12 with the emission reducing unit 15. The transmitting/receiving device 12 is connected at the connection ends 121, 122 to a bus 40, more precisely to a first bus core 41 of the bus for CAN _ H and to a second bus core 42 of the bus for CAN _ L. Due to the bus signal CAN _ H, CAN _ L, a differential bus signal VDIFF = CAN _ H-CAN _ L appears on the bus 40. The

bus conductors

41, 42 are terminated at their ends by a terminating resistor 48, as is only very schematically depicted in fig. 2. At the transmitting/receiving device 12, a voltage Supply, in particular a CAN Supply (Supply), for the first and

second bus conductors

41, 42 is realized via at least one connection 123. The connection of the transmitting/receiving device 12 to ground or CAN GND is effected via the connection 124.

In the case of the transmitting/receiving device 12, the first and

second bus conductors

41, 42 are connected to a transmitting stage, also referred to as a transmitter, and have transmitting

blocks

125, 126. Even if this is not shown in detail in fig. 2, the first and

second bus conductors

41, 42 are also connected to a receiving stage 120, which is also referred to as a receiver, in the case of the transmitting/receiving device 12. Only the elements of the transmit stage are shown in more detail in fig. 2, while the receive stage 120 together with its receive comparator 1200 is shown very schematically, since the more detailed construction of the receive stage and the receive comparator is already known and is not necessary for the elucidation of the present embodiment.

A driver circuit 127 for driving a transmission signal TxD, which is generated by the communication control device 11 and is output to the transmission/reception device 12, is connected to the transmission blocks 125, 126 and thereby to the transmission stage. The transmission signal TxD is also referred to as TxD signal. Depending on the information to be transmitted, the transmit signal TxD may have different voltage states, in particular a recessive state 110 or a dominant state 111.

According to fig. 2, the transmitting stage has a first transmitting block 125 for the signal CAN _ H of the first bus line 41 and a second transmitting block 126 for the signal CAN _ L of the second bus line 42. The transmission stage also has a reverse-polarity protection diode 128 between the connection 123 for the voltage supply and the first transmission block 125. A reverse polarity protection diode 129 is connected between the connection 122 for the second bus line 42 and the second transmit block 126.

The first transmit block 125 has a low voltage PMOS transistor 1251 (PMOS = P-type metal oxide semiconductor) and a P-channel high voltage isolation transistor 1252 in series. A parasitic capacitance 1253 is formed between the gate and the drain of the P-channel high voltage isolation transistor 1252. The capacitor 1253 is also referred to as the gate-drain capacitance of the P-channel high voltage isolation transistor 1252. Thus, a capacitor 1253 is formed between the gate of the transistor 1252 and the connection 121 for the first bus line 41.

The second transmit block 126 has a low voltage NMOS transistor 1261 (NMOS = N-type metal oxide semiconductor) and an N-channel high voltage isolation transistor 1262 in series. A parasitic capacitance 1263 is formed between the gate and drain of the N-channel high voltage isolation transistor 1262. The capacitor 1263 is also referred to as the gate-drain capacitance of the N-channel high voltage isolation transistor 1262. Thus, a capacitor 1263 is formed between the gate of the transistor 1262 and the cathode of the reverse polarity protection diode 129, which reverse polarity protection diode 129 is provided for the connection 122 of the second bus line 42.

If one of

subscriber stations

20, 30 transmits a transmission signal TxD onto bus 40, the dynamics of the signal of transmitting

subscriber station

20, 30 causes a current I _ CAN _ H, I _ CAN _ L in

bus connections

121, 122 of receiving transmit/receive device 12 of subscriber station 10. The current I _ CAN _ H, I _ CAN _ L flows here predominantly through the parasitic gate-

drain capacitances

1253, 1263 of the associated

isolation transistors

1252, 1262 at the

connections

121, 122 for the signals CAN _ H and CAN _ L. In the event that the emission reduction unit 15 is not operating, the current I _ CAN _ H flowing into the connection 121 of the bus conductor 41 for the signal CAN _ H during the switching process due to the changeover between the

different states

111, 110 of the transmission signal TxD becomes significantly greater than the current I _ CAN _ L flowing into the connection 122 of the bus conductor 42 for the signal CAN _ L. This leads to different currents in the decoupling network according to fig. 3 and, as a result, to radiation levels which are too high for EMC authentication.

To avoid this, according to fig. 2, an emission reducing unit 15 is connected to the gate of a P-channel high-voltage isolation transistor 1252. The emission reduction unit 15 has a logic block 151 for switching on or off a low-ohmic switch 152 in the form of an N-channel transistor. A high ohmic resistor 153 can be connected between the gate and drain of N-channel transistor 152, which is connected at one end to the gate of P-channel high voltage isolation transistor 1252 and at the other end to ground. Resistor 153 may be a single resistor. Alternatively, the resistor 153 may be formed of at least two resistors connected to each other.

The transmission reducing unit 15 implements an isolation device that switches in the transmission block. In this case, the on path for the N-channel high voltage isolation transistor 1252 is grounded low-ohmic or high-ohmic, as specified by the logic block 151, as described subsequently.

In the case of a subscriber station of the subscriber station 10 which is to receive in the transmission/reception device 12 in the bus system 1, i.e. which is not to transmit itself, the gate of the N-channel high-voltage isolation transistor 1252 is connected to ground via the high-ohmic resistor 153 as specified by the logic block 151 and is thereby connected to ground at a high-ohmic point. Thus, resistor 153 is connected into the on path of transistor 1252, which is an isolation device. As a result, the current I _ CAN _ H flowing into the connection 121 for the bus signal CAN _ H during switching of the bus signal on the bus 40 decreases strongly. The current I _ CAN _ H flowing into the connection 121 for the bus signal CAN _ H is thus adapted to the current I _ CAN _ L flowing into the connection 122 for the bus signal CAN _ L for the case mentioned.

For the case that the transmitting/receiving device 12 of the subscriber station 10 in the bus system 1 is intended to implement a transmitting subscriber station and the bus 40 is intended to be driven for the dominant bus state due to the dominant state 111 of the transmit signal TxD, a high-ohmic gate connection would disadvantageously impair the switching-time behavior of the bus signal. Thus, logic block 151 decides in the case of such a send instruction: the gate of the N-channel high voltage isolation transistor 1252 is grounded by means of the low ohmic switch 152 and thereby to the low ohmic ground. Thus, switch 152 is connected in the on path of transistor 1252, which is an isolation device. If the transmit/receive apparatus 12 is to ascertain the recessive level both at its output of the receive comparator 1200 in the receive stage 120 and also at the transmit signal TxD, the switch 152 is kept high-ohmic, so that the gate of the N-channel high-voltage isolation transistor 1252 is connected to ground at high-ohmic via the resistor 153 by means of the low-ohmic switch 152.

Thus, the transmission/reception apparatus 12 causes: the different currents I _ CAN _ H, I _ CAN _ L, which are caused by the significantly larger P-channel isolation device, transistor 1252, at connection 121 for bus conductor 41 compared to the N-channel isolation device, transistor 1262, at connection 122 for bus conductor 42, are compensated. The P-channel isolation device is chosen to be significantly larger than the N-channel isolation device so that the two devices have the same resistance Rdson in the on-state. In this case, the effect of the parasitic gate-

drain capacitances

1253, 1263 is compensated for by these

devices

1252, 1262 and by the reverse polarity protection diode 129, which has to be plugged in the CANL path of the transmit stage due to the requirement of the CAN specification of maximum rating-27V.

With the decoupling network 50 according to fig. 3 on the two

bus cores

41, 42 of the bus 40, the transmission can be measured for the transmitting/receiving

devices

12, 13. The decoupling network 50 has a first series circuit formed by a first capacitor 51 and a first resistor 52. The resistor 52 is connected at its other end to the first bus conductor 41 for the bus signal CAN _ H. The decoupling network 50 also has a second series circuit of a second capacitor 53 and a second resistor 54. The resistor 54 is connected at its other end to the second bus line 42 for the bus signal CAN _ L. The first and second capacitors 51, 53 are each connected at their other end to a resistor 55, which is connected at its other end to ground. A voltage measuring device 58 is connected in parallel with the resistor 55.

As shown in fig. 3, the bus 40 ends with a resistance 48 between the two

bus wires

41, 42. The voltage V _ CAN _ Supply for the transmitting/receiving

devices

12, 13 is fed from the connection 60.

The transmitting/receiving means 12 of the

subscriber stations

10, 30 are each connected to the bus line 41 at a connection 121. Furthermore, the transmission/reception devices 12 are each connected to the bus conductors 42 at a connection 122. The

terminals

123, 124 of the transmit/receive unit 12 are occupied, as described above in relation to fig. 2.

Similarly, the transmitting/receiving means 13 of the subscriber station 20 is connected to the bus line 41 at a connection 131. Furthermore, the transmitting/receiving device 13 is connected to the bus conductor 42 at a connection 132. The voltage V _ CAN _ Supply for the transmitting/receiving device 13 is fed at the connection 133. At the connection 134, the transmitting/receiving device 12 is connected to the ground of the bus system 1, in particular to CAN _ GND.

The configuration shown in fig. 3 and described above corresponds to the configuration specified in the document IEC TS 62228 integrated circuits — EMC evaluation of CAN transmitters in the case of EMV measurements. The three transmitting/receiving

devices

12, 13 therefore operate on the same CAN bus 40 with a common terminating resistor 48 having a resistance value of 60Ohm and a decoupling network 50. One of the transmitting/receiving devices 12 transmits in a controlled manner via a transmission signal TxD1, while the other transmitting/receiving

devices

12, 13 are in the same operating mode but do not transmit an explicit bit or an explicit signal state, so that their respective transmission signals TxD2, TxD3 are high = recessive (rezensv). A special case of this is shown in figure 3.

By means of the respective transmission reduction unit 15 in the transmitting/receiving device 12, a reduced current I _ CAN _ H is generated, which is adapted to the smaller current I _ CAN _ L flowing to the bus pins or

connections

121, 122, 131, 132 of the two receiving transmitting/receiving

devices

12, 13, as described above with regard to the transmitting/receiving device 12.

The resulting emissions with respect to the transmitting/receiving device 12 are shown in fig. 4 as a function of the instantaneous decoupling voltage V1(t) over time t. In fig. 5, for comparison, the instantaneous decoupling voltage V2(t) over time t is also shown for the transmitting/receiving device 13 without the transmission-reduction unit 15. The signal waveform according to fig. 5 has a high amplitude in the range of the resonance frequency of the common mode choke. The signal waveform according to fig. 4 shows a significantly reduced amplitude, i.e. a reduction of the amplitude by a factor of 3 to 4.

The current I _ CAN _ H, I _ CAN _ L flowing into the

connections

121, 122 CAN therefore be adapted significantly in the decoupling network 50 by means of the transmission reduction unit 15 in the transmitting/receiving device 12. As a result, the transmission of the two transmitting/receiving devices 12 according to fig. 4 is significantly lower than the transmission of the transmitting/receiving device 13 according to fig. 5. Thus, during EMV authentication and also during later operation of the transmitting/receiving device 12, the strongly excessively high radiation levels that can be measured in the case of the transmitting/receiving device 13 according to fig. 5 do not occur.

The effect on the frequency spectrum is shown in fig. 6 for the respective transmitting/receiving device 12 and in fig. 7 for the transmitting/receiving device 13. According to fig. 7, the requirement of 55dB μ V in the range of 750kHz to 10MHz is severely violated for the transmitting/receiving device 13. In contrast, this requirement can be met in the case of the respective transmitting/receiving device 12, as can be seen from fig. 6.

Thus, in the case of the transmitting/receiving device 12, the method for reducing wired transmission is implemented by means of the transmission reduction unit 15.

According to the second embodiment, the size of the N-channel high voltage isolation transistor 1252 can be reduced, which reduces the coupling capacitance 1253. This is strongly limited by power loss considerations in the event of a short circuit, for example of a battery pack, on the bus 40 with respect to the vehicle. Because of this, in order to follow the transmission level tolerance, the CMOS components of the N-channel high-voltage isolation transistor 1252 should also be increased (CMOS = Complementary Metal-Oxide-Semiconductor = Complementary Metal Oxide Semiconductor).

All of the previously described embodiments of the transmission reduction unit 15 of the transmitting/receiving device 12, of the

subscriber stations

10, 30, of the bus system 1 and of the methods implemented therein according to the first and second exemplary embodiments can be used individually or in all possible combinations. In addition, the following modifications are conceivable in particular.

The previously described bus system 1 according to the first and second embodiments is described in terms of a bus system based on the CAN protocol. However, the bus system 1 according to the first and/or second embodiment may be other types of communication networks. It is advantageous, but not mandatory, to ensure exclusive, collision-free access of a

user station

10, 20, 30 to the bus 40 or to a common channel of the bus 40 in the bus system 1 at least for certain time intervals.

The bus system 1 according to the first and/or second exemplary embodiment and modifications thereof is in particular a CAN network or a CAN-HS network or a CAN FD network or a Flex Ray network. However, the bus system 1 may be other serial communication networks.

The number and the arrangement of the

subscriber stations

10, 20, 30 in the bus system 1 according to the first and second embodiments and their modifications are arbitrary. In particular, only subscriber station 10 or subscriber station 20 or subscriber station 30 may be present in the bus system 1 of the first or second embodiment. Independently of this, there may be only one emission reduction unit 15 which is designed according to one of the previously different design variants.

The functionality of the previously described embodiments may be implemented in a transceiver or transmitting/receiving

device

12, 13 or a transceiver or a CAN transceiver or a set of transceiver chips or a set of CAN transceiver chips or the like. Additionally or alternatively, the chipset may be integrated into an existing product. It is possible in particular that: the functions considered are either implemented in the transceiver as a separate electronic module (chip) or embedded in an integrated overall solution, in which case there is only one electronic module (chip).

Claims

1. A transmitting/receiving device (12) for a bus system (1), having:

a transmission stage (121) for transmitting a transmission signal (TxD) to a first bus core (41) of a bus (40) of the bus system (1), an exclusive, collision-free access of a subscriber station (10, 20, 30) to the bus (40) of the bus system (1) being ensured at least at times in the bus system (1), and for transmitting the transmission signal (TxD) to a second bus core (42) of the bus (40);

a receiving stage (120) for receiving a bus signal (CAN _ H, CAN _ L) transmitted on a bus core (41, 42); and

a transmission reduction unit (15) for controlling a switch-on path of a first isolation device (1252) in the transmission stage depending on whether a dominant state (111) of the transmission signal (TxD) is present.

2. The transmit/receive apparatus (12) of claim 1, wherein the emission reduction unit (15) is designed to control the effective resistance with respect to ground for the on-path of the P-channel isolation device (1252).

3. The transmitting/receiving device (12) according to claim 1 or 2,

wherein the sending stage has: a first transmission block (125) for transmitting the transmission signal (TxD) to the first bus core (41); and a second transmission block (126) for transmitting the transmission signal (TxD) to the second bus line (42) and

wherein the first isolation device (1252) is connected into the first transmit block (125).

4. The transmit/receive apparatus (12) as claimed in one of the preceding claims, wherein the first isolation device is a P-channel isolation transistor (1252), and wherein the emission reduction unit (15) is designed to control a gate of the P-channel isolation transistor (1252).

5. The transmit/receive apparatus (12) of claim 3 or 4, wherein a second isolation device (1262) is provided in the second transmit block (126), the second isolation device being smaller than a first isolation device (1252) provided in the first transmit block (125).

6. The transmit/receive apparatus (12) of claim 5, wherein the second isolation device (1262) is an N-channel isolation transistor (1262).

7. The transmitting/receiving device (12) according to one of the preceding claims, wherein the emission reduction unit (15) has:

a logic block (151) for analyzing the transmission signal (TxD) and a signal (CAN _ H, CAN _ L) received from the bus (40);

a resistor (153) connected at one end to the gate of the isolation device (1252) and at its other end to ground; and

a switch (152) for switching the gate of the isolation device (1252) depending on the result of the analysis of the logic block (151) such that the gate of the isolation device (1252) is either grounded low-ohmic by means of the switch (152) or grounded high-ohmic via the resistor (153).

8. The transmitting/receiving device (12) according to claim 7,

wherein the logic block (151) is designed to: when a dominant state (111) of the transmission signal (TxD) occurs, the switch (152) is actuated in order to connect the switch-on path of the isolation device (1252) to ground with low resistance, and

wherein the logic block (151) is designed to: when the recessive state (110) of the transmit signal (TxD) occurs and a transmit/receive device (12) of a subscriber station (10) is operated for receiving but not transmitting, the switch (152) is actuated in order to connect the switch-on path of the isolation device (1252) to high-ohmic ground.

9. The transmitting/receiving device (12) according to claim 4 or 5,

wherein the switch (152) is a transistor having a resistance value lower than the resistance (153) ohm, and

wherein an output of the logic block (151) is connected to a gate of the transistor.

10. The transmit/receive device (12) according to one of the preceding claims, wherein the transmit/receive device (12) is a CAN FD transmit/receive device (12).

11. A bus system (1) having:

a bus (40); and

at least two user stations (10; 20; 30) which are connected to one another by means of the bus (40) in such a way that they can communicate with one another,

wherein at least one subscriber station of the at least two subscriber stations (10; 20; 30) has a transmitting/receiving device (12) according to one of the preceding claims.

12. Method for reducing wired transmissions, wherein the method is carried out with a transmitting/receiving device (12) for a bus system (1) in which exclusive, collision-free access by a user station (10, 20, 30) to a bus (40) of the bus system (1) is ensured at least at times, wherein the transmitting/receiving device (12) has a transmitting stage, a receiving stage (120) and a transmission reduction unit (15), wherein the method has the following steps:

-transmitting a transmission signal (TxD) to a first bus core (41) of the bus (40) with the transmission stage;

-transmitting the transmission signal (TxD) to a second bus core (42) of the bus (40);

-receiving, by means of the receiving stage (120), a bus signal (CAN _ H, CAN _ L) transmitted on a bus core (41, 42); and also

-controlling, by means of the transmission reduction unit (15), a switch-on path of a first isolation device (1252) in the transmission stage depending on whether a dominant state (111) of the transmission signal (TxD) is present.